Two-cycle airplane engine



J. W. DAVIS TWO CYCLE AIRPLANE ENGINE Filed Dec. 22, 1927 Sept. 3, 1929. 1,727,051

Patented Sept. 3, i929.

UNITED STATES JOHN- W. DAVIS, OF WASHINGTON, "DISTRICT OF COLUMBIA.

- TWO-CYCLE AIRPLANE ENGINE.

Application filed December 22, 1927. Serial No. 241,937.

'This invention relates to airplane engines and particularly to two cycle cam en'gmes. It is generally realized and admitted that no engine can deliver its maximum horsepower per pound weight unless it be operated on the two cycle principle. However, all

airplane engines to date have been of the four cycle type because the two stroke cycle has presented numerous problems which have heretofore prevented satisfactory operation. For a clear understanding of this invention therefore it is necessary to enumerate the drawbacks heretofore innate in two cycle engines.

Rear compression has been used so that control of the fuel charge could not. be POSI', tively had. Abutments could not be so built as to block off the space under a'piston and thereby force all the fuel charge into the combustion chamber. Or if an auxiliary piston and cylinder is used it must be of the same size or larger than the main cylinder thereby elfe'cting no saving in weight. Thus no means have been heretofore built for a portable engine whereby any saving in weight together with proper fuel charge feeding could be had. Uneven delivery of power is fatal in an airplane engine. 3

Another drawback has been that a port has been used for exhaust gases, the port being adapted to be uncovered on the downward stroke of the piston. The high heat of the gases together with their great velocity tends to burn up the walls adjacent to the port so that even if this port were built very heavy poor results are had due to burning up of lubricating oil, warping of the I cylinder, scaling and rusting upon cooling and preigniting the fuel.

Another drawback comes in preignition or a waste of fuel or both. The fuel charge has generally been used for scavenging, pushing the exhaust gases outahead. This contact of the fuel with the hot gases tends to preignite the charge or at least to heat the charge whereby a volumetric loss of fuel is had. If the exhaust gases were driven completely out some fuel would have to accompany it, or if a slight bit of exhaust ases were left in the cylinder a loss would t en occur. A scavenging pump causes extra weight, additional moving parts and more expense.

In addition'to this trouble has been had in cooling the piston, the interior becoming so hot as to warp the iston or at least to cause preignition of the c arge.

Of course, many suggestionsas to how to overcome all these difficulties have been patented, but obviously are all failures as far as solving the entire problem is concerned.

With these things and others in mind it is the object of this invention to provide a two cycle engine adaptable for airplane use. For this purpose I have chosen a cam engine for reasons which will presently become apparent.

It will be readily seen that with a two cycle cam engine will be produced two thrusts on the propeller shaft at points 180 apart. This motion cannot be had with any other type of engine and I therefore especially recommend it therefor/but do'not in any way limit my invention to this type of engine because it can be well adapted and applied to anyairplane engine whether of the radial,

V or longitudinal type. The thing that makes my invention possible is the speed of the air past a cylinder carriedby an airplane. I utilize this high air speed for scavenging purposes. No fuel enters at the scavenging time hence preignition of the charge is "prevented because 110, fuel is in contact with the exhaust gases. Suppose that the plane will travel at 90 miles per hour when the engine is turning up 2000 R. P. M. 2000 divided by 60 33 or 1/33 of a second elapses per revolution. By using an elongated base circle portion of a cam as more fully explained in my copending application Serial Number 243,792, filed December 31, 1927, I allow a 90 arc of. the cam circle for scavenging time. I discount some of this time agalnst 1nert1a of the gases which is further taken into account by realizing that if a plane is traveling 90 miles per hour the speed of the air past the cylinder is greater than 90 miles per hour because no propeller can be 100% eflicient. Thus I have approximately 1/5 of a circle (90=%) for scavening. 1/5 X 1/33 gives 1/165 of a see. as actual scavenging time. The speed of the air is 90 M. P. H. which is 132 feet per second. During 1/165 of a second therefore the air will travel 132/165 feet or 9.6 inches. The stroke of no airplane engine built or contemplated to date exceeds seven inches. Therefore the air from the propeller blast will scavenge the cylinder with 2.6 inchesto spare. While I have taken 90 M. P. H. at 2000 R. P. M. as an example it will readily be seen that ,this principle will hold true over a wide range of speed and for all engines except those of the very high speed type. I have thus provided means for using a force en= tirely outside of the engine proper because it is a mere coincident that an engine speed will produce a travel speed proportionate to scavenging time. The fact that this has been entirely overlooked heretofore is mainly responsible for failure of anycompany to attempt the building of a two .cycle' air'plane engine, although this one .fact alone will not make a two cycle engine practical. It might also be said in this connection thatthe tendency is toward slow speed engines for air- 7 plane use due to less vibration and longer life. The problems of high speed engines are too numerous to mention here and it suffices to call attention to the wide application of the invention revealed and claimed herein.

Inconsidering the drawback of the burnt exhaust passage it will be notedfhat I employ a puppet valve located in the head of the en- The air' which drives out the exhaust gases,

, of course, fills the cylinder. I cutoff the air supply when this condition exists and by the use of a small pump, force a fuelcharge composed of a rich mixture from the carburetor. This pump'is capable of sending in the exact charge desired and I therefore control the fuel at all times. 7

The cooling of the piston is partially cared for by permitting the cold air blast from the propeller to pass directly over and against the piston head. Air at high velocity is a wonderful convector of heat but an extremely poor conductor. Thus on the old type en-" gines where an abutment on the head merely directed air upwardly contact was not had by the major portion of the piston with the air 01; fuel and in addition a high velocity was not had. J

My invention will be more fully understood with reference to the accompanying drawings in which Fig. 1 represents a longitudinal section thru a cam engine. I

Fig. 2 represents a transverse section thru a cam engine along line 2-2 of Fig. 1.

Referring more particularly to the drawings, 1 refers to the crankcase of a cam engine adapted to be supported by frame mem-' bers 2.- 3 indicates the cylinders in the head of which is mounted an exhaust valve cage 15 containing-exhaust valve 4 and ret-ained 'by spring 16. The exhaust valve 4 is actuated by a rocker arm 17 held by a support 18, which is in turn actuated by a push rod 19 resting against a tappet 20 which is intermitposed of two cans, 9 and 10, adaptedto revolve in opposite directions and driving the shaft 8 in connection with gearing 12, 13 and 14, and more fully set forth in my copending application, Serial Number 241,807, filed December 22, 1927, and is merely shown by way of illustration but forms no part of this invention.

Cylinder 3. has contained therein apiston 6 carrying rollers 7 and 7 adapted to act against and drive cams 9 and 10 butthe rollers might be replaced by-a connecting rod and the cams by'a crank. At or near the lowest position of piston 6 I form a port 21 extending a material distance around said sylinder and having any desired width. A flared portion 22 leads from the port for the purpose of making available alarge volumeof air. The flared portion 22 is turned directly into the air blast from the propeller which is termed the slipstream. Exhaust pipe 30 emits gases in the reverse direction. Preferably on the opposite side of the cylinder is mounted an auxiliary cylinder 5 in which is a piston 23 having a piston rod 24'carrying two rollers 25 and 25' which rollers are adapted to ride in a groove of a cam 26. The exact shape of the cam track will control the speed andperiod of operation of the .piston 23. 27 indicates the x, fuel inlet which leads from a carburetor not shown. A valve 28 controls communication between the pump and the combustion chamber. Valve 28 may be any type of check valve having a seat in the side of the pump cylinder instead of the engine cylinder so that in case of sticking it will not be sheared by the piston 6. The cylinder port forms a nozzle, injecting fuel upwardly and tangentially. It is desirable to'have a small cut out portion 29 so that the major portion of the pump may force all fuel outof cylinder 5 on each stroke. I

desire to position cylinder 5 very close to the engine cylinder and have the line joining the cylinders very short as shown. However in cases where this arrangement may not be deemed best, it would not depart from the" spirit of the invention to have each, pump cylinder supply two cylinders by using it as a double acting pump or even in having one pump supply four cylinders by running it twice as fast by varying the cam track and also using it as double acting. Also by making the pump a little larger'than diagrammatically shown it may replace the supercharger and function as a supercharger and charge injector also. There are so many different duties for an airplane engine that Ido not desire to be limited as far as structural III details are concerned. A plane-built for speed would involve variations from one built for freight carrying and Itherefore de-.

plane engine which consists in releasing the exhaust gases immediatel prior to the end of the power stroke, admitt ng air from the slip stream directly into said engine at the end of the power stroke and in introducin fuel into said air following emission of t eexhaust gases.

2. a two cycle airplane engine, means comprising a valve for releasing exhaust gasesnear the end of the power stroke, means comprising a port for admitting air into said engine directly from the slipstream at the end of theipower stroke part of said air act- I ing as scavenging means andpart acting as a fuel support and means for injecting fuel into said engine. 7

3, In a twocycle airplane engine, a cylinder, a piston and an exhaust valve in said cylinder, a port adapted to be uncovered by said piston during the lower portion of its power stroke, said port admitting air for scavenging at the velocity caused by the speed of said plane andof the propellerdriving said plane and 'a fuel pump for delivering a rich mixture into the air remaining in said cylinder after scavenglng.

4. In a'two cycle cam engine a cyllnder, an

exhaust port adapted to be opened prior to the end of the power stroke, means comprising an-elongated base portion of said cam for permitting a long scavenging period, a port adapted to be held open during said scavenging period, said port adapted to admit air and a fuel pump adapted to admit fuel during the compression stroke.

5. he combination as set forth in claim 4, said air being admitted directly into said cylinder from the slipstream. i

6. The combination as set said air being usedboth for scavenging for forming a fuel supporter.

7. The combination as set forth in claim 4, said pump acting both as a fuel pump and as a supercharger.

8. In a .two cycle enginet for airplanes means for releasing the burnt gases, means for introducing air from the slip stream immediately upon reduction of pressure in the cylinder, said air scavenging the cylinder and forth in claim 4, and

forming a charge for use with fuel, and'means r r i JOHN w. DAvIs 

